The present invention relates generally to variable valve actuating mechanisms and, more particularly, to a spring guide for use with a variable valve actuating mechanism.
Variable valve actuating mechanisms enable the variation of the timing, lift and duration (i.e., the valve lift profile) of associated valves, such as, for example, the valves of an internal combustion engine. Two examples of variable valve actuating mechanisms are detailed in commonly-assigned U.S. Pat. No. 5,937,809 and 6,019,076, the disclosures of which are incorporated herein by reference.
As related to internal combustion engines, conventional variable valve mechanisms are associated with a cam or input shaft of the engine. More particularly, a conventional variable valve mechanism typically includes a roller which engages an input cam of the input shaft or the engine camshaft. The roller is linked to an output cam, such as, for example, by one or more link or rocker arms. Rotation of the input cam displaces the roller and thereby creates oscillatory movement of the linking components. The oscillatory movement of the linking components, in turn, directly or indirectly oscillate the output cam, which, in turn, actuates one or more associated valves of the engine.
Many conventional variable valve actuating mechanisms incorporate a biasing means, such as one or more return springs, that biases the output cam toward its starting position. The return spring is compressed as the output cam is oscillated counter-clockwise from its starting position in order to actuate or open the associated valve, and expanded or decompressed during the closing of the associated valve. The expansion or decompression force of the spring returns the output cam to its starting position. Typically, the return springs are flat or non-curved helical springs, i.e., the centerline or central axis of the spring is substantially straight. Flat springs have a natural frequency or mode of vibration, often referred to as spring surge, that is generally directed along the central axis of the flat spring. The maximum operational frequency of the mechanism is limited to approximately eight to ten times less than the natural frequency of the flat or non-curved spring.
Curved springs are generally semicircular in shape, i.e., have a curved central axis relative to which the spring coils are substantially concentric. The use of a curved spring in a variable valve actuating mechanism has the advantage of saving space and/or eliminating a link or return bar. However, curved springs have an inherent additional vibrational mode or natural frequency which is not found in any significant magnitude in a flat or non-curved spring. This additional vibrational mode or natural frequency of a curved spring occurs in the middle-most coils of the curved spring in a direction that is generally perpendicular to the plane of the curved spring central axis, and is substantially lower than the natural frequency of the spring surge in a flat or non-curved spring. Due to this additional, lower natural frequency of a curved spring, the maximum operational frequency of a variable valve actuating mechanism having a curved return spring is only a fraction, i.e., approximately one-half to three-fourths, of the maximum operational frequency of the same mechanism using a flat or non-curved spring.
In an effort to compensate for the lowered maximum operational frequency of a variable valve actuating mechanism having a curved spring, external spring guides can be used. Such external guides generally surround the periphery of the spring, and thus consume additional space and/or volume. Furthermore, such external spring guides have a radius that is larger than the spring which they are guiding, and are therefore subject to relatively large frictional forces and relatively large torque hysteresis.
Therefore, what is needed in the art is a device that permits the use of a curved spring at greater maximum frequencies of compression and expansion.
Furthermore, what is needed in the art is a device which reduces the amplitude of the additional mode of vibration or natural frequency of a curved spring.
Even further, what is needed in the art is a device which increases the limited maximum operational frequency of a variable valve actuating mechanism having a curved spring.
Still further, what is needed in the art is a spring guide device that occupies less space and/or volume than a conventional external spring guide.
Moreover, what is needed in the art is a spring guide device that reduces frictional forces and torque hysteresis relative to an external spring guide device.
The present invention provides an internal spring guide for use with a curved spring.
The invention comprises, in one form thereof, an elongate, curved guide member having a centerline. The centerline has a centerline curvature that is substantially equal to a radius of curvature of the curved spring. The guide member includes a first side having a side curvature. The side curvature is substantially equal to a curvature of the curved inside surfaces of the coils of the curved spring. The guide member is configured for being disposed within the curved spring such that the coils thereof substantially surround a periphery of the guide member.
An advantage of the present invention is that it permits the use of a curved spring at greater maximum frequencies of compression and expansion.
Another advantage of the present invention is that it increases the limited operational frequency of a variable valve actuating mechanism having a curved spring to approximately the same maximum operational frequency of a variable valve actuating mechanism incorporating a flat spring.
Yet another advantage of the present invention is that it occupies less space and/or volume than is occupied by a conventional external spring guide.
A still further advantage of the present invention is that it reduces frictional forces and torque hysteresis relative to an external spring guide device.
Sill further advantages of the present invention will be obvious to one skilled in the art and/or appear hereinafter.